The Ogallala Aquifer - a nearly 174,000-square-mile underground cache of water that spreads across parts of Kansas, Texas, Oklahoma, Colorado, Nebraska, New Mexico, South Dakota, Texas and Wyoming - is one of the largest freshwater aquifers in the world.
The Ogallala, part of the High Plains Aquifer, is composed mainly of silt, sand, gravel, and clay - rock debris that washed off the face of the Rocky Mountains and other more local sources over the past several million years, according to the Kansas Geological Survey.
One of the primary sources of water for agriculture areas in these states, it is also one of the fastest depleting aquifers. Irrigation pioneers who first tapped into the reserve to sustain their crops believed the water supply was inexhaustible.
By the 1950s, there were more than 80 wells a year being dug in Colorado alone. Additionally, according to Kansas State University, about 1 million acres were under irrigation in Kansas by 1960.
Now, the abundance of irrigation wells is threatening the once-abundant reserve. Water by the hundreds of gallons per minute is being pumped out of the ground in some places, with recharge not coming close to refilling it.
According to a U.S. Geological Survey report released in 2009, the Ogallala has shrunk 9 percent across the eight-state region since the advent of irrigation. In Kansas, some pockets have declined by more than 150 feet since pre-development.
Typical declines in southwest and west-central Kansas are 50 to 150 feet. The rates of drawdown and recharge of the aquifer vary from location to location, largely, in part, because the depth of the aquifer and the natural thickness varies, according to the Kansas Geological Survey.
Moreover, some areas have suffered deeper drops in a short period. In an graphic developed by The Hutchinson News, several southwest Kansas wells monitored by the Kansas Geological Survey have declined by 50 to 100 feet in a decade.
By Kansas law, water is a public resource dedicated to the use of the people of the state. Individuals, companies, municipalities and others can obtain permission to use water for beneficial purposes by obtaining a water right, said Brownie Wilson, with the Kansas Geological Survey.
Kansas water law is based on the doctrine of prior appropriation, he said.
Thus, according to the law, when there is insufficient water to meet all water rights, the date of the water right determines who has the right to use the water. This doctrine is commonly expressed as "First in time, first in right."